The present invention relates to a magnetic cell and a magnetic memory, and more particularly, it relates to a magnetic cell and a magnetic memory which can be written-in by passing spin-polarized electrons.
Conventionally, in order to control the direction of magnetization of a magnetic material, the method of applying a magnetic field to the magnetic material has been taken. For example, in the case of the hard disk drive, writing-in is carried out by reversing the magnetization direction of a medium by applying a magnetic field generated from a recording head. Moreover, in a solid-state magnetic memory, the magnetization direction of a cell is controlled by applying a current-induced magnetic field generated by passing a current to the wirings provided near the magnetoresistance effect elements including the cell. The magnetization direction control by the external magnetic fields has old history, and can be taken as an established technology.
On the other hand, in the recent progress of the nanotechnology, the miniaturization of the magnetic substance has been carried out rapidly, and it has been required to perform the magnetization control with nano-scale and locally. However, since the magnetic field fundamentally has the character to spread over a space, it is difficult to be made localized. As the size of a recording bit or a cell becomes minute, when selecting a specific recording bit or a specific cell and controlling the magnetization direction, the problem of a “cross talk” that a magnetic field reaches to a next bit or a next cell becomes remarkable. Moreover, if a generation source of the magnetic field is made small for the sake of making the magnetic field localized, the problem that the generating magnetic field can not be obtained enough will arise.
Recently, “Direct-current-driving magnetization reversal” in which the magnetization reversal is carried out by passing a current to a magnetic material is disclosed by F. J. Albert, et al., Appl. Phy. Lett. 77, 3809 (2000).
The magnetization reversal by a current is the phenomenon that the angular momentum of the spin-polarized electrons generated when the spin-polarized current passes magnetic layers cause reversal of magnetization by transmitting and acting on the angular momentum of the magnetic material whose magnetization is to be reversed. By using this phenomenon, it becomes possible to act on the magnetic material with nano-scale and also to record to a minuter magnetic material.
However, currently, there is a problem that the reversal current required to reverse a magnetization is as large as 10 mA through several mA when the size of a cell is in a range between 100 nm and several 10 nm. That is, the magnetic cell structure where required current for the magnetization reversal is as small as possible is required in order to prevent a destruction of the element by the current, and to prevent a generation of heat and to reduce power consumption.